Rotary solenoids of this type are drives based on the electro-magnetic principle where instead of a longitudinal motion the result is a rotational motion. Rotary solenoids of this type, for example, are known as rotational proportional solenoids that perform a rotational movement proportional to the current flow because of the current flow through the windings.
If the current flow through the winding of the coil conducting the current is switched off, the rotor is supposed to return in its starting position. For this purpose it is known in the state of the art providing a spring against the spring force of which the rotational motion is performed when the current is switched on, and the stored spring energy of which serves for resetting the rotor when the current is switched off. Employing appropriate return springs is often not convenient as assembling the springs requires additional space in the rotary solenoid. Furthermore, there is the risk that the return spring breaks and then the entire rotary solenoid fails. Just with rotary solenoids of small constructional dimensions assembling the filigree return spring is often very laborious and also prone to errors, what increases often the costs for manufacturing.